The present invention relates generally to solid state rechargeable battery and vehicle propulsion. More specifically, the present invention provides a method and system for an all solid-state rechargeable battery and a vehicle propulsion system powered by the battery. Merely by way of example, the invention has been applied to a vehicle propulsion system, but there may be a variety of other applications.
Liquid and particulate based energy storage systems are known. That is, rechargeable electrochemical storage systems have long been employed in automotive and transportation applications, including passenger vehicles, fleet vehicles, electric bicycles, electric scooters, robots, wheelchairs, airplanes, underwater vehicles and autonomous drones. Rechargeable electrochemical storage systems with liquid or gel electrolytes are commonly used in these applications in order to take advantage of their relatively high ionic diffusivity characteristics. Different anode and cathode half-cell reactions have been deployed, that can be categorized into conventional lead-acid, nickel-cadmium (NiCd), nickel-metal-hydride (NiMH), and Lithium-ion (Li-ion).
For example, conventional lead acid batteries contain electrodes of elemental lead (Pb) and lead oxide (PbO2) that are submersed in a liquid electrolyte of sulfuric acid (H2SO4). Rechargeable NiMH batteries typically consist of electrodes that are submersed in a liquid alkaline electrolyte such as potassium hydroxide. The most common type of rechargeable Li-ion batteries typically consist of electrodes that are submersed in an organic solvent such as ethylene carbonate, dimethyl carbonate, and diethyl carbonate that contain dissolved lithium salts such as LiPF6, LiBF4 or LiClO4. In lithium-ion polymer batteries, the lithium-salt electrolyte is not held in an organic solvent but in a solid polymer composite such as polyethylene oxide or polyacrylonitrile.
Liquid electrolytes generally require a non-conductive separator in order to prevent the shorting of the rechargeable battery cell. Microporous polymer separators are usually used in combination with liquid electrolytes so that lithium ions are permitted to pass through the separator between the electrodes but electrons are not conducted. However, these separators are relatively expensive and the source of defects and often detract from the energy density of the finished product.
Another problem with the use of organic solvent in the electrolyte is that these solvents can decompose during charging or discharging. When appropriately measured, the organic solvent electrolytes decompose on the initial charging and form a solid layer called the solid electrolyte interphase (SEI), which is electrically insulating, yet provides sufficient ionic conductivity.
These liquid or polymer electrolyte rechargeable electrochemical storage systems can be connected in series or in parallel in order to make additional voltage or current available at the pack level. Electrified drivetrain systems may demand power delivery in the range of 2 horsepower to 600 horsepower and they may require energy storage in the range of 1 kWh to 100 kWh, depending upon the needs of the vehicle, with power needs of over 1000 W/kg.
In order to meet these energy and power requirements while obtaining sufficient safety, the existing art teaches towards fabrication of smaller cathode particles, even in the nano-scale, such as the LiFePO4 nano-material that is being marketed by A123 Systems. These smaller nanoparticles reduce the transport distance any particular Li-ion needs to travel from the liquid electrolyte to reach the interior most point of the cathode particle, which reduces the generation of heat and stress in the cathode material during the charge and discharge of the battery. Therefore, it would be unexpected to one of ordinary skill in the art who is making battery cells for applications other than low discharge-rate microelectronics that a cathode film where the smallest axis is over one micron thick would create a viable product. Conventional manufacturers of rechargeable battery cells for electric vehicles and portable electronics generally prefer to select cathodes heterogeneous agglomerations comprised of nano- and micro-scaled particles that are mixed in a wet slurry and then extruded through a slotted die or thinned via a doctor blade, whereupon subsequent drying and compaction results in an open-cell, porous structure that admits liquid or gel electrolyte to permeate its pores providing intimate contact with the active material.
In addition, the conventional technique suggests that rectangular, prismatic cells such as those utilized by A123 Systems, Dow Kokam, LGChem, EnerDel and others in their electric vehicle battery packs must be contained in a pack that has foam or other compressible materials between the cells. The conventional technique teaches that over the lifetime of a large automotive battery pack these cells will undergo swelling, and foam or another compressible material is required to be used as a spacer between these battery cells in order to maintain sufficient pressure in the beginning of the pack's lifetime but which will also yield as the cells swell. The conventional technique also teaches compression bands or another mechanical mechanism to keep the external battery pack casing from opening as the cells swell. The conventional technique also teaches that pressure on the battery cells is required to assure good performance, putatively because of the maintenance of good contact and thus low contact resistance and good conductivity in the battery cells.
At the pack level, the conventional technique teaches that complex controls are needed to manage packs of battery cells, particularly to manage the unknown lifetimes that result from side reactions in agglomerated particulate cells between the active materials in combination with liquid or cell electrolytes at temperature extrema or at state-of-charge minima or maxima ranges. For example, these controls architectures typically possess algorithms that combine voltage monitoring with coulomb-counting mechanisms to estimate the current state-of-charge of each individual cell that is contained in the battery pack. Each cell may then be operated at the voltage and current of the cell that is measured to have the lowest voltage and charge in order to maintain cell lifetime and reduce the probabilities of a thermal runaway. Packs which are constructed from a plurality of cells named in this invention may not require such complex controls architectures due to the higher uniformity at the particle and cell level from alternate manufacturing techniques.
Existing solid state batteries such as those described in U.S. Pat. No. 5,338,625 have been developed that utilize a solid, often ceramic, electrolyte rather than a polymer or a liquid. However, public research of these electrolytes has shown that they are widely known to suffer from relatively low ionic conductivities (see “Fabrication and Characterization of Amorphous Lithium Electrolyte Thin Films and Rechargeable Thin-Film Batteries”, J. B. Bates et al. Journal of Power Sources, 43-44 (1993) 103-110. In this invention, the inventors have used computational models they invented to determine the materials layer thicknesses and configurations that are optimal, knowing the ionic conductivity and diffusivity properties that are measured in the electrolyte, anode, and cathode materials of materials they have fabricated and which are in the literature. Furthermore, these solid-state batteries are typically produced on relatively small areas (less than 100 square centimeters) that limit the total capacity of the cell in Ampere-hours (Ah).
For example, the largest battery cell in the thinergy line of solid state battery product that is currently produced by Infinite Power Solutions is stated to contain 2.5 mAh of total capacity in a package that has dimensions of 25.4 mm×50.8 mm×0.17 mm and a maximum current of 100 mA at a nominal voltage rating of 4.1 volts. These solid state battery cells have a nominal energy density of only 46.73 Wh/L which are far below the industry norm of 200-400 Wh/L for comparable Li-ion liquid electrolyte cells. In addition, the miniscule capacity of these cells that results from their design and the choice of utilizing a batch production process means that it would take over 1,500,000 of these cells connected in series and in parallel in order to achieve a pack with net nominal energy storage of at least 16 kWh, which is the energy storage capacity of a typical extended range electric vehicle (EREV) such as the Chevrolet Volt. Existing solid-state battery cell designs and fabrication processes therefore are impractical for inclusion in an electric vehicle drivetrain.
Moreover, these small solid-state batteries suffer from low energy density at the product scale due to a relatively large mass ratio of pack to active materials. Additionally, existing solid-state batteries are often made using expensive and low-rate methods such as sputtering and chemical vapor deposition (CVD). Other faster processes have been hypothesized, such as chemical bath deposition (CBD), but remain to be proven. These faster processes may reveal difficulties in producing uniform products with defect rates that are low enough to be tolerable to the transportation industry.
The selection of the substrate material is another important differentiator in the product that has been designed by the inventors. To date, practitioners of solid state batteries have selected substrates which are able to be annealed and which may be more robust during further packaging steps, such as ceramic plates, silicon wafers, metallic foils, and thicker polymer materials such as polyimides which are greater than 8 to 10 microns thick and which have high heat tolerances. None of these materials currently being used are available in gauges that are less than 5 to 10 microns thick. In contrast, in this invention the inventors have selected to pair a thinner polymer substrate, under 10 microns, which is not capable of being annealed.
Clearly, this trend leads to inherent problems in the current practice of device design and manufacturing. Accordingly, it is seen that there exists a need for an apparatus and method to produce an improved solid state battery for large scale production.